1) Field of the Invention
The present invention relates to a Stirling engine and a hybrid system that uses the Stirling engine.
2) Description of the Related Art
Stirling engine is an external combustion engine, i.e., in the Stirling engine, a working fluid is heated from outside. The Stirling engines are advantageous over other engines. For example, they has high thermal efficiency. Moreover, in Stirling engines, various types of alternative energies can be effectively used as a heat source for heating the working liquid. For example, even the low temperature difference energies such as solar energy, geothermal energy, or exhaust heat can be used as a heat source, which allows for energy saving.
Japanese Utility Model Application Laid-Open Publication (JP-U) No. H04-89836 discloses a conventional Stirling engine. This Stirling engine is shown in FIG. 21. In this Stirling engine, a high-temperature side cylinder 121 and a low-temperature side cylinder 122 protrude from a machine room 120. One end of a heater 123 is connected to the upper part of the high-temperature side cylinder 121, and the other end is connected to a regenerator 125. A radiator 126 is connected to both the low-temperature side cylinder 122 and the regenerator 125. An expansion piston 127 reciprocates in the high-temperature side cylinder 121 while a compression piston 128 reciprocates in the low-temperature side cylinder 122. The expansion piston 127 and the compression piston 128 are linked to a crankshaft 131 with connecting rods 129 and 130, respectively. Therefore, both the expansion piston 127 and the compression piston 128 reciprocate while mutually having a predetermined phase difference, for example, of 90 degrees.
The heater 123 includes a heat source (not shown) for heating a working fluid. When the working fluid is heated, the working fluid expands. The expansion piston 127 is pressed due to the pressure exerted by the expanded working fluid, which causes a pivotal movement of the crankshaft 131. When the expansion piston 127 is in up stroke position, the working fluid passes through the heater 123 to the regenerator 125. The regenerator 125 includes a heat storage material. The working fluid heats the heat storage material in the regenerator 125 and subsequently flows into the radiator 126 where it is cooled. In the radiator 125, the working fluid is compressed when the compression piston 128 is in up stroke position. The compressed working fluid flows back toward the heater 123 via the regenerator 125 and the heater 123. The working fluid is heated and it expands while it passes through the regenerator 125 and the heater 123.
In the Stirling engine, a space for a heat exchanger including the heater, the regenerator, and the radiator is an invalid capacity that is not directly dedicated to output. An increase in the volume of the heat exchanger results in a decrease in output of the Stirling engine. Therefore, it is desired to make the heat exchanger compact. However, a compact heat exchanger does not perform the heat-exchange effectively. Therefore, if a compact heat exchanger is used, then the engine output decreases.
As explained above, making the heat exchanger compact is contradictory to the increase in the engine output, and therefore, it is necessary to increase efficiency of the heat exchanger in order that the two are made compatible. Therefore, it is desirable to increase the efficiency of the heater.
Some of the Stirling engines are made to operate on exhaust heat such as exhaust gas from an internal combustion engine. However, if such Stirling engine is installed under environments in which it is difficult to ensure sufficient heat, it becomes necessary to efficiently use the available heat.
When the exhaust gas is used to heat the Stirling engine, the place where the Stirling engine can be installed becomes limited. For example, the Stirling engine needs to be installed adjacent to a pipe that carries the exhaust gas from the internal combustion engine. Since there is little space is such places, the Stirling engine must be compact.
Another conventional Stirling engine is disclosed in JP-U No. H04-89836. In this Stirling engine, a high-temperature cylinder and a low-temperature cylinder are arranged in a V-shape. Moreover, a radiator and a regenerator are provided in parallel with the high-temperature cylinder, and a heater is provided between the regenerator and the high-temperature side cylinder. However, because of the V-shape, the Stirling engine becomes bulky and requires more space for installing. Furthermore, the low-temperature cylinder and the radiator are connected to each other at almost a right angle, which is a disadvantage in a channel resistance (flow loss) of the working fluid.
Japanese Patent Application Laid Open Publication (JP-A) No. 2000-146336 also discloses a V-shaped Stirling engine.
JP-U No. H06-60751 and JP-A No. H05-5479 disclose conventional Stirling engines in which a high-temperature cylinder and a low-temperature cylinder are arranged in series. In these Stirling engines, no countermeasures have been taken to efficiently use heat under environments in which it is difficult to ensure sufficient heat. There is also a problem on the channel resistance of the working fluid.